What is Aqua-Wax?
Quick answer: Aqua Wax is a spray-on wax used on a freshly washed, still-wet car. Mist onto wet panels, spread with a damp microfibre and dry off; it leaves a slick, glossy, hydrophobic layer. Quick and safe over coatings, but durability is weeks rather than years.
Aqua Wax is a branded product by AutoGlym, but the name is often used for the whole category of sprays applied to the car after washing but before drying.
It is a very quick way to wax a car and has been common practice with contract valeters for years, who might clean and wax thirty cars in a day. A trade favourite is bright orange and usually called "Tango".
These products are all easy to use and leave a shiny finish across paint, glass, chrome, plastics and rubber. They do not offer long-lasting protection, but that is not really the point -- the assumption is that you will reapply every time you wash. In that sense they are close cousins of wash'n'wax.
They are also what gets pumped through automated car washes. If you select "hot wax" or similar at the jet wash, this is the kind of product you are getting.
Chemically, most aqua waxes are blends of synthetic polymers, waxes and surfactants tuned to behave properly on wet panels. They are perfectly safe over a cured ceramic coating, but they will not extend the coating's life -- if anything, the wax residue can mute the coating's hydrophobic behaviour and mask how it is actually performing. So if you have a coating and like the look of aqua wax, by all means use it; just know that the "protection" you are adding is short-lived and largely cosmetic.
For how aqua wax compares to other protection options, see is there anything better than a ceramic coating?